How to pretty print JSON string using Jackson?

The following example demonstrates how to pretty print the JSON string produces by Jackson library. To produce well formatted JSON string we create the ObjectMapper instance and enable the SerializationFeature.INDENT_OUTPUT feature. To enable this feature we need to call the enable() method of the ObjectMapper and provide the feature to be enabled.

ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
String json = mapper.writeValueAsString(recording);
System.out.println(json);

On the second example below we format unformatted JSON string. To do this we use the ObjectMapper‘s readValue(String, Class<T>) method which accept the JSON string and Object.class as the value type. The readValue() method return an Object. To format the JSON object we call mapper.writerWithDefaultPrettyPrinter().writeValueAsString(Object). This will produce a pretty formatted JSON.

ObjectMapper mapper = new ObjectMapper();
Object jsonObject = mapper.readValue(json, Object.class);
String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject);
System.out.println(prettyJson);

Below is the complete code snippets.

package org.kodejava.example.jackson;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.io.IOException;
import java.time.LocalDate;
import java.time.Month;

public class JsonIndentOutput {
    public static void main(String[] args) {
        JsonIndentOutput.formatObjectToJsonString();
        JsonIndentOutput.formatJsonString();
    }

    private static void formatObjectToJsonString() {
        Recording recording = new Recording();
        recording.setId(1L);
        recording.setTitle("Yellow Submarine");
        recording.setReleaseDate(LocalDate.of(1969, Month.JANUARY, 17));
        recording.setArtist(new Artist(1L, "The Beatles"));
        recording.setLabel(new Label(1L, "Apple"));

        ObjectMapper mapper = new ObjectMapper().enable(SerializationFeature.INDENT_OUTPUT);
        try {
            String json = mapper.writeValueAsString(recording);
            System.out.println(json);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }

    private static void formatJsonString() {
        String json = "{\"id\":1,\"title\":\"Yellow Submarine\",\"releaseDate\":\"1969-01-17\",\"artist\":{\"id\":1,\"name\":\"The Beatles\"},\"label\":{\"id\":1,\"name\":\"Apple\"}}";
        ObjectMapper mapper = new ObjectMapper();
        try {
            Object jsonObject = mapper.readValue(json, Object.class);
            String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonObject);
            System.out.println(prettyJson);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The code snippet above will pretty print the following JSON string:

{
  "id" : 1,
  "title" : "Yellow Submarine",
  "releaseDate" : "1969-01-17",
  "artist" : {
    "id" : 1,
    "name" : "The Beatles"
  },
  "label" : {
    "id" : 1,
    "name" : "Apple"
  }
}

Here are the structure of Recording class.

package org.kodejava.example.jackson;

import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import java.time.LocalDate;
import java.util.Objects;

public class Recording {
    private Long id;
    private String title;

    @JsonDeserialize(using = LocalDateDeserializer.class)
    @JsonSerialize(using = LocalDateSerializer.class)
    private LocalDate releaseDate;

    private Artist artist;
    private Label label;

    public Recording() {
    }

    public Recording(Long id, String title, LocalDate releaseDate) {
        this.id = id;
        this.title = title;
        this.releaseDate = releaseDate;
    }

    // Getters and Setters
}

Maven Dependencies

<!-- http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.8.6/jackson-databind-2.8.6.jar -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.6</version>
</dependency>

How to read and write Java object to JSON file?

The following example demonstrate how to serialize and deserialize Java object to JSON file. The Jackson’s ObjectMapper class provides writeValue(File, Object) and readValue(File, Class<T>) methods which allow us to write an object into JSON file and read JSON file into an object respectively.

package org.kodejava.example.jackson;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;
import java.io.IOException;

public class ObjectToJsonFile {
    public static void main(String[] args) {
        Artist artist = new Artist();
        artist.setId(1L);
        artist.setName("The Beatles");

        ObjectMapper mapper = new ObjectMapper();

        File file = new File("artist.json");
        try {
            // Serialize Java object info JSON file.
            mapper.writeValue(file, artist);
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Deserialize JSON file into Java object.
            Artist newArtist = mapper.readValue(file, Artist.class);
            System.out.println("newArtist.getId() = " + newArtist.getId());
            System.out.println("newArtist.getName() = " + newArtist.getName());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The result of the code snippet are:

newArtist.getId() = 1
newArtist.getName() = The Beatles

Maven Dependencies

<!-- http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.8.6/jackson-databind-2.8.6.jar -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.6</version>
</dependency>

How to convert JSON string to Java object?

In the following example we will convert JSON string to Java object using ObjectMapper class from the Jackson library. This class provides a method readValue(String, Class<T>) which will deserialize a JSON string into Java object. The first argument to the method is the JSON string and the second parameter is the result type of the conversion.

package org.kodejava.example.jackson;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

public class JsonToObject {
    public static void main(String[] args) {
        String json = "{\"id\": 1, \"name\": \"The Beatles\"}";

        ObjectMapper mapper = new ObjectMapper();
        try {
            Artist artist = mapper.readValue(json, Artist.class);
            System.out.println("Artist = " + artist);

            System.out.println("artist.getId() = " + artist.getId());
            System.out.println("artist.getName() = " + artist.getName());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The code snippet above will print to following output:

Artist = Artist{id=1, name='The Beatles'}
artist.getId() = 1
artist.getName() = The Beatles

Maven Dependencies

<!-- http://repo1.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.8.6/jackson-databind-2.8.6.jar -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.8.6</version>
</dependency>